A technology has spread in recent years that uses images captured by a plurality of cameras installed on the circumference of a movable body and that displays an overhead (bird's eye) view that includes the image of the movable body taken from above or displays a 360-degree panoramic image by combining images. To convert the image captured by the camera into an overhead view, or the like, or to display a panoramic image by combining images, the parameters that are used include the positions (coordinates x, y, and z) of the camera, the angles (the depression angle ψ, the rotation angle φ, and the pan angle θ) of the camera, and the like.
To install a camera on a movable body, because each parameter of the camera is different depending on the installation condition and because of installation errors, calibration needs to be performed in order to correctly determine each parameter of the camera. The camera, which is installed on the movable body, is calibrated by using a special jig before shipment. However, the parameters of the camera gradually change due to degradation with aging after shipment and due to degradation of the area where the camera is installed.
For example, a change in the angle of the camera changes the result of calculating the distance between the camera and an object that is extracted from the image, which results in the incorrect displaying of an overhead image or panoramic image. Therefore, it is desirable to calibrate the camera after shipment. Because it is difficult to use a special jig after shipment, it is preferable to calibrate the camera without using a special jig.
A disclosed technology for performing calibration after shipment involves extracting the right and left white lines of the straight road along which the movable body is moving and calibrating the camera by using the extracted white lines. Another well-known technology involves calibrating the camera by using the geometric shape of a sign painted on the road surface.
Japanese Laid-open Patent Publication No. 2003-329411
Japanese Laid-open Patent Publication No. 2001-225709
Japanese Laid-open Patent Publication No. 2008-11174
Japanese Laid-open Patent Publication No. 2000-11133
Japanese Laid-open Patent Publication No. 2004-205398
The above-described conventional technology is based on the assumption that the road surface is flat in the image captured by the camera and that the white line or the painted sign satisfies an assumed shape. If these assumptions are not satisfied, there is a problem in that the conventional technology is not used.
Even if the white line or the painted sign satisfies the assumed shape, the conventional technology is not also used when the white line or the painted sign is concealed by a different vehicle. In an actual traffic environment, a situation often occurs where the white line or the painted sign is distorted or is concealed by a different vehicle.
Therefore, there are many situations where calibration is not performed even if a parameter of the camera is incorrect; thus, calibration is not correctly performed.